Cutting old toilet waste pipe

[smudge.g]

Good evening from a very new member,
I recently bought a victorian Scottish farmhouse which is being redecorated very slowly. We are currently improving an originally awful yellow 1930s understairs toilet and having removed the old loo, I need to shift the waste pipe close to the wall to enable a nice new combined unit to be fitted. However, having broke through the concrete floor to get to the pipe below floor level, I have found that the pipe is cast iron (looks abut 3.5 inch diameter). What i dont know is, is it safe to cut through this rusted (and i guess quite thick) iron pipe to reduce the length so that a plastic waste elbow can be fitted, that will lie closer to the wall? Our sewage system is septic tank, being a rural location but I dont know whether this could cause problems with cutting pipes. I have access to an angle grinder that may do the trick but wanted to ask advice before trying this. I have included a rather dark image, that shows the pipe, wall is to the left and present loo connection on right. i am looking to try and remove the whole elbow and fitting a new plastic pipe closer to the wall, before refilling and concreting over. The other issue is whether there are plastic pipes that are compatible with these old iron pipes as they do seem to be a universal diameter these days.
thanks in advance for any assistance and happy Christmas to all for next week.

 

[Lime]

Once you remove what is attached to the metal elbow it may come loose on the horizontal pipe if you try to turn/twist the elbow.
(It depends on what has been used to seal the joint)
However take care not to stress the cast iron pipe too much as it could crack.
Cast iron is incredibly strong in compression (many times stronger than steel) but very weak in tension.
From your picture it appears that the collar is the wrong way round i.e. the collar is on the elbow and not the horizontal pipe (it is not all that clear, I might be wrong), but that should make the elbow easier to remove.
A judicious tap on the collar with a soft hammer in the direction it comes off may loosen it.

The problem when using an angle grinder on cast iron is that the metal is inflexible and does not bend (it will crack if you try to bend it when cut part-way through) so you have to cut through all the metal you wish to remove before applying force to remove it.

 

[stuart45]

You can hire chain pipe cutters that will cut cast iron pipes. You can get a fitting for a 3.5 internal measurement cast to plastic.

 

[smudge.g]

Good evening all,
thanks for the tips/advice. In the end the job was fairly straight forward with use of an angle grinder (although access was very limited) and a chisel/hammer to finish of the cut as couldnt get the grinder down that far. With the use of a 3.5 to 4inch plastic pipe adapter and flex-hose to pan connector, hopefully the job will be finished tomorrow and we can at last make use of our nice new (old refurbished) loo!!!
regards